The present invention relates generally to engine testing, and more specifically, to a stationary test stand for supporting an aircraft gas turbine engine during power testing.
Aircraft gas turbine engines include various rotors having blades rotating therewith such as fan, compressor, and turbine blades which generate vibratory excitation forces during operation. Accordingly, the engine is conventionally designed to maximize the margin between the various operational excitation frequencies and the critical frequencies associated with the natural resonance modes of vibration to minimize undesirable vibration and to obtain acceptable engine life.
The vibratory response of the engine is typically affected by its supporting structure in the aircraft. For example, an aircraft engine is typically mounted to an aircraft wing by a conventional pylon. The combination of the aircraft wing and pylon have inherent flexibilities in each of the six spatial degrees of freedom.
During the development of an aircraft gas turbine engine the various stator and rotor components thereof must be designed to obtain suitably low vibration during operation. In order to be certified for an aircraft application, the engine is tested for vibratory response to ensure acceptable vibratory levels. Upon completion of the certification program and during production of the engines, each engine is typically tested before shipment in a conventional stationary test stand to ensure acceptably small levels of vibration.
A typical test stand includes a vertical support column suitably mounted to a foundation in the ground, with a head frame at the top thereof from which individual aircraft engines are mounted for testing. During ground testing, the engine is operated at various levels of output power thrust and various components thereof are monitored for vibration levels. Conventional test stands typically include a removable adapter which mounts the engine and pylon to the test stand head frame for allowing ready assembly and disassembly of the engine to the test stand.
One problem with this arrangement is that the test stand itself and the test stand adapter are rigid structures having a spring constant much greater than that of the stiffness of the airframe (e.g. wing and/or pylon). Therefore, the loads and vibration characteristics experienced by the engine in testing does not have perfect fidelity.